On Fri, Feb 23, 2018 at 04:02:27PM +0800, Huang, Ying wrote:

[off-list ref] writes:
[snip]

quoted

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 39ae7cfad90f..c56cce64b2c3 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c

@@ -332,32 +332,38 @@ struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
 			       unsigned long addr)
 {
 	struct page *page;
-	unsigned long ra_info;
-	int win, hits, readahead;
 
 	page = find_get_page(swap_address_space(entry), swp_offset(entry));
 
 	INC_CACHE_INFO(find_total);
 	if (page) {
+		bool vma_ra = swap_use_vma_readahead();
+		bool readahead = TestClearPageReadahead(page);
+

TestClearPageReadahead() cannot be called for compound page.  As in

PAGEFLAG(Readahead, reclaim, PF_NO_COMPOUND)
	TESTCLEARFLAG(Readahead, reclaim, PF_NO_COMPOUND)

quoted

 		INC_CACHE_INFO(find_success);
 		if (unlikely(PageTransCompound(page)))
 			return page;
-		readahead = TestClearPageReadahead(page);

So we can only call it here after checking whether page is compound.

Hi Huang,

Thanks for cathing this.
However, I don't see the reason we should rule out THP page for
readahead marker. Could't we relax the rule?

I hope we can do so that we could remove PageTransCompound check
for readahead marker, which makes code ugly.